The present invention relates to airfeed drills; more particularly, the present invention relates to airfeed peck drills.
Airfeed peck drills have found their greatest utilization in the aerospace industry. This is because airfeed peck drills have the ability to drill accurate holes with a fine surface finish. Heretofore it was thought that airfeed peck drills were best used when drilling deep holes in thick material (depth to diameter ratios or 7:1 or greater).
A typical design for an airfeed peck drill is shown in U.S. Pat. No. 4,123,188. The extended length of the airfeed peck drill taught in the '188 patent embodies what was thought to be the necessary technology to make an airfeed peck drill operate. Specifically, it was thought that the drill quill containing the air motor and reduction gearing must be moved by an air cylinder attached to the back end of the drill quill. To control drill travel a follower arm was mounted to the back of the cylinder. The follower arm was used to engage a damping cylinder. This damping cylinder then controlled the feed rate of the drill quill towards the workpiece.
Because of the movement of the rotating drill in and out of the hole being formed in the workpiece, it is essential that the travel of the rotating drill be closely confined to exactly the same path or else any slight wobble or displacement of the rotating drill would cause the hole to be formed out of round or to be formed in a skewed manner. Consequently, any forces or extensions from the drill quill were positioned so as to not cause and deflection of the drill quill as it neared the mouth of the hole being drilled. Additionally it was felt that all forces exerted in a direction parallel to the drill quill should be as co-linear to the central axis of the drill quill as possible. Such constraints led to the long, lengthly design of airfeed peck drills. While satisfactory in their performance, it was found that such long airfeed peck drills were limited in their application due to their excessive length. When these long airfeed peck drills were mounted to a fixture for the drilling of a hole a moment arm was created by the drill itself. This moment arm coupled with the weight of the unit would then cause improperly drilled holes, particularly in smaller or thinner workpieces, due to fixture deflection.
There is therefore a need in the art to provide an airfeed peck drill which does not have the long length of prior art drills such that airfeed peck drills may be used without the need for heavy massive fixturing.